Spread butter on one side of each slice of bread. Flip over 4 slices of bread and layer each with some of the quince paste, manchego, Cheddar, crushed almonds and blue cheese crumbles. Top with another slice of bread.
Heat a square, flat griddle pan over medium heat. Place the sandwiches on the griddle pan and dome with a metal bowl. Cook until golden brown on the bottoms, then flip, dome and repeat until the insides are gooey and the outsides are golden, 8 to 10 minutes total. Cut on the bias and serve.